The present invention relates to air duct insulation sheets and similar products and to a coating process for coating such products. The air duct insulation sheets and similar products of the present invention have multilayered coatings. These multilayered coatings are applied by a coating process wherein discrete layers of the coating can be specifically formulated to provide the multilayered coating with specific performance characteristics, such as but not limited to, a first layer specifically formulated to provide the multilayered coating with puncture resistance and a second layer formulated to provide the multilayered coating with abrasion resistance.
Fibrous insulation batts and blankets and foam insulation sheets are used as thermal and acoustical insulation in a variety of products such as but not limited to heating, ventilating and air conditioning (HVAC) duct liners, HVAC duct boards, and automotive hood liners. As used herein, the terms xe2x80x9csheetxe2x80x9d or xe2x80x9csheetsxe2x80x9d include both continuous lengths of insulation, such as but not limited to glass fiber blankets typically ranging in length up to about 200 feet and in width from about 3 to 8 feet, and shorter length insulation batts, blankets or boards, such as but not limited to, glass fiber insulation batts, blankets or boards typically ranging in length up to about 10 feet and in width from about 3 to 8 feet.
With respect to HVAC products, such as glass fiber or foam duct liners and duct boards the major surfaces of these insulation sheets which are exposed to the air flow through the air ducts are typically coated with elastomeric coatings. These elastomeric coatings provide relatively smooth interior surfaces on the air ducts that reduce the frictional resistance of the air ducts to the flow of air through the air ducts and the accumulation by the air ducts of airborne dust, particles, viruses, bacteria and pathogens that tend to accumulate in irregularities in the interior surface of the air ducts. In addition, on the fibrous insulation sheets, the elastomeric coatings retard or substantially eliminate the separation of fibers or dust from the fibrous insulations by the flow of air through the air ducts.
The air duct insulation sheets are normally coated on one major surface (the surface which will become the exposed interior surface of the air duct) with an elastomeric aqueous cross-linkable emulsion composition such as an acrylic emulsion. Typically, the elastomeric cross-linkable composition is frothed or foamed prior to its application over the irregular and uneven surface of the insulation sheet in order to form a uniform coating on the major surface of the insulation sheet. When the coating is heat cured, the exposure of the emulsion coating composition to the heat causes the coating composition to lose water and the frothed or foamed coating to collapse (i.e. coalesce and eliminate bubbles from the froth or foam). The heat curing also causes the elastomeric resins of the coating to cross link to a tough thin coating that covers the major surface of the insulation sheet. By way of example, U.S. Pat. No. 4,990,370, issued Feb. 5, 1991, On-Line Surface and Edge Coating of Fiber Glass Duct Liner, discloses one method of applying such coatings to insulation sheets; U.S. Pat. No. 5,211,988, issued May 18, 1993, Method for Preparing a Smooth Surfaced Tough Elastomeric Coated Fibrous Batt, discloses another method of applying such coatings to insulation sheets; and U.S. Pat. No. 5,487,412, issued Jan. 30, 1996, Glass Fiber Airduct With Coated Interior Surface Containing a Biocide, discloses such coatings wherein a biocide is included in the coating to retard or prevent microbiological growth on the interior surface of an air duct.
While these methods of applying coatings to insulation sheets and the insulation sheets produced by these methods perform well, there has remained a need to provide a method of coating insulation sheets and, in particular air duct insulation sheets, that gives the producer greater flexibility in the coating process to improve the coating produced and/or reduce manufacturing costs.
The method of the present invention forms a multilayered coating on an insulation sheet wherein the coating composition of each discrete layer of the multilayered coating can be specifically formulated to provide the multilayered coating with specific and distinct performance characteristics and/or to reduce costs and each discrete layer can be formed to the thickness required to perform its particular function. Thus, the coated insulation sheets of the present invention, with their multilayered coatings can each be specifically designed to provide required performance characteristics for particular applications with the opportunity to save on manufacturing costs through the formulation of the coating compositions used for different layers and the regulation of the amount of coating materials used to form the different layers.
The method of the present invention is an on-line method of forming a multilayered coating on an insulation sheet in which a first coating layer (e.g. a layer of a first foamed or frothed cross-linkable elastomeric aqueous emulsion coating composition) is applied directly to and substantially uniformly over a first major surface of the insulation sheet. An exposed major surface of the first coating layer is heated to only partially cure and stabilize the coating composition at the exposed major surface of the first coating layer so that the first coating layer remains an essentially discrete layer when a second coating layer is applied to the exposed major surface of the first coating layer and so that a second coating layer applied to the exposed major surface of the first coating layer will readily bond to the first coating layer. A second coating layer (e.g. a layer of a second foamed or frothed cross-linkable elastomeric aqueous emulsion coating composition) is applied directly to and substantially uniformly over the exposed major surface of the first coating layer subsequent to heating the exposed major surface of the first coating layer. The insulation sheet and the first and second coating layers, are heated subsequent to the application of the second coating layer, until the first and second coating layers are substantially dried and cured.
While other coatings can be used, the preferred coating compositions used to form the multilayered coatings of the present invention are cross-linkable, elastomeric aqueous emulsions, such as aqueous acrylic emulsions. A cross-linkable emulsion contains monomers and polymers, some of which have multiple polymerizable sites to effect cross-linking to a three dimensional polymer. The formulations of the coating compositions forming each layer of the multilayered coatings of the present invention can each be distinct and specifically formulated to perform a desired function that enhances the performance of the insulation sheet for its intended application. For example, the first layer can be formulated to be more puncture resistant while the second layer can be formulated to be more abrasion resistant or to include a biocide. In addition, each layer of the multilayered coatings can be formed to the specific thickness desired or required to perform its particular function and control production costs.
Coated insulation sheets are typically cured in convection ovens where the convection currents of hot gases can disturb the exposed surface of the coating to make the surface rougher or more irregular. To provide a smoother exposed surface on the outermost layer of the multilayered coating of the finished product, the exposed surface of the outermost layer of the multilayered coating can be heated (e.g. by infrared heaters or a hot ironing surface), without disturbing the smooth exposed major surface of the outermost coating layer, to stabilize the smooth major surface of the outermost coating layer prior to heating the insulation sheet and the coating layers by convection heating until the first and second coating layers are substantially dried and cured.